1. Field of the Invention
The present invention relates to an optical disk apparatus and a recording/reproducing method used in the apparatus, and more particularly to a substituting process for a double-sided recordable optical disk.
2. Description of the Related Art
A format of an optical disk is first described. FIG. 8 shows an exemplary format of an optical disk including a spare area. In FIG. 8, the downward direction indicates the direction from an inner side to an outer side of the tracks, and the transverse direction indicates the direction in which sectors are arranged.
As is shown in the figure, an area from the (0)th track to the (i)th track is a map area 801 for recording information on the substituting process. The area from the (i+1)th track to the (j)th track is a data area 802 for recording the usual recording data. The area from the (j+1)th track to the (k)th track is a spare area 803 in which, if the data area 802 includes any defective sectors, alternative sectors which alternatively record information to the defective sectors are located. An area from the (k+1)th track to the (n)th track is map area 804.
When data is to be recorded on a rewrite optical disk, a laser beam irradiation is performed for one and the same sector usually twice or three times. In the case of an optical disk capable of overwriting, the first irradiation is performed for retrieving a target address in the data area 802 and for recording the data into the target sector. The second irradiation is performed for reading out the data recorded at the target address in order to verify the recorded data. In the case of an optical disk which is not capable of overwriting, a laser beam irradiation for erasing the target address is performed before the data is recorded.
When any recording error occurs during this recording operation, e.g., when an error occurs in the verification, or when data is not properly recorded because any abnormality such as a track jump error or an address read error occurs in the recording, the target sector to which data is recorded is treated as a defective sector, and a substituting process for recording the data into the alternative sector in the spare area 803 is performed. In the case where such a substituting process is performed, a flag indicating that the sector is a defective sector is written into that defective sector. Then, information specifying the alternative sector to which data is recorded alternatively to the defective sector is recorded in the map area 801. As is shown in FIG. 8, the map areas 801 and 804 are usually located at a plurality of positions in the most inner periphery and in the most outer periphery of the optical disk. In order to enhance the reliability, the same information is multi-recorded. When the data for which the substituting process is performed is to be reproduced, the information on the substituting process recorded in the map area 801 is first read out, so that the CPU recognizes the address of the alternative sector in which the data is actually recorded. Then, the retrieval order is grasped and an optical head is controlled so as to read out the data.
Now assuming the case where, in an optical disk apparatus capable of recording or reproducing data simultaneously for both sides by using a double-sided recordable optical disk, and having a structure in which optical head moving systems for both sides cooperatively operate in the radius direction of the optical disk, and a defective sector exists in either one side of the double-sided recordable optical disk in the recording, and the substituting process of the defective sector is performed for only one side. When the recorded data that is to be reproduced and hence the alternative sector for which the substituting process is performed is to be read out, the optical head for the other side on which the substituting process is not performed is also positioned in the alternative area. Accordingly, it is necessary for a user to wait for a period in which the reading operation is interrupted on the side for which the substituting process is not performed. As a result, the data reproducing process time is disadvantageously increased.